1. Field of Invention
This invention relates to a composition for reducing the viscosity of polymeric materials. More particularly, the instant invention relates to the reduction of the viscosity of polyacrylates which are employed in radiation curable coating compositions.
2. Prior Art
Polyacrylate esters of polyglycidyl ethers have been particularly useful in protective coatings because of their rapid cure rates, high degree of toughness and good chemical resistance. However, their extremely high, neat viscosity has been a serious drawback, particularly in those photocurable systems where the presence of a solvent would significantly increase cure time. Because nearly all polyacrylates of polyglycidyl ethers are resinous and of extremely high viscosity--often approaching 2,000,000 cps--some solvent or diluent must usually be employed. This is especially so when polyacrylates are used in radiation curable compositions.
Several approaches have been employed in the prior art to find a solution to the viscosity problem of radiation curable systems. For example, inert volatile organic solvents and the more volatile monomeric reactive diluents have been added to these polymers in an effort to reduce their viscosity. In addition, the structure of the oligomer backbone has been modified such as by end capping secondary hydroxyl groups using vinyl ethers.
However a number of problems are encountered when the viscosity reduction procedures of the prior art are employed. Such procedures can add additional and expensive steps in the manufacturing process or can adversely affect the curing properties of the composition. In addition, the introduction of some materials into the composition to reduce viscosity can cause a separation of the composition into resin and diluent phases. And when secondary hydroxyl groups are chemically blocked, undesirable by-products that must be removed are often produced. Furthermore the solvents used to reduce viscosities of these polymeric compositions to an acceptable level when evaporated cause pollution of the environment. Hence, it is desirable to reduce the amount of solvent used or to use environmentally safe solvents, such as water. Moreover, additional energy is required to remove solvents added to the composition.
U.S. Pat. No. 4,425,472 discloses that the incorporation of water in amounts insufficient to form a stable water-in-oil emulsion is effective in reducing the viscosity of radiation curable compositions containing at least one olefinically unsaturated polymeric material. The use of water in accordance with this patent allegedly reduces the viscosity without adversely affecting the curable composition or its curing properties. However, the viscosities obtained by the addition of water are still well in excess of satisfactory levels.
Accordingly, an object of this invention is to reduce the viscosity of polyacrylates.
It is another object of this invention to reduce the viscosity of radiation curable compositions and to facilitate handling without adversely affecting the curing properties of the compositions.
These and other objectives are obtained by preparing the compositions of the instant invention.